The overall goal of the proposed experiments is to demonstrate that neuronal operations can be meaningfully interpreted within the concept of intrinsic reference frames. To this effect, the realization of reference frames in the eye and head movement system of vertebrates will be studied in a behavioral context, as will their phylogenetic and ontogenetic development. The first specific aim will be to determine the process of sensory-motor transformation in the vestibulo-ocular reflex system and the involved neuronal circuits. The second project will establish the structure-function relationship of vestibular neurons to compensatory and voluntary eye movements in all three dimensions of physical space. The third specific aim will be to describe the ontogenesis of the optokinetic reference frame within the retino-cerebello-vestibulo-oculomotor loop, using dark-reared animals. The fourth specific aim targets the phylogenetic development of the vertebrate vestibulo-oculomotor system, in particular the acquisition of a horizontal semicircular canal by gnathostomes and the prototypical bony fish and elasmobranch oculomotor organization. The fifth specific aim will be to investigate further the biomechanics of the vertebrate head-neck ensemble, extending this study to the human head movement system. Completion of this particular project may yield useful data in regard to orthopedic and neuronal disorders involving the cervical vertebral column. Experimental techniques utilized in this research include acute and chronic animal preparations, three-dimensional visual and vestibular stimuli with extraand intracellular recordings, extra- and intrdcellular horseradish peroxidase (HRP) histochemistry, three-dimensional eye movement recordings with the magnetic search coil technique, cineradiography, and selective lesions of labyrinthine endorgans. As a long-term goal, the proposed experiments should demonstrate that the brain utilizes intrinsic reference frames to reduce the degrees of freedom of sensory-motor systems, thus simplifying neuronal operations, as well as economizing brain function in light of a narrow window of optimal brain-to-body ratio.